1. Field of the Invention
The present invention relates generally to test equipment as used in manufacturing semiconductor and electronic devices, and more specifically to precision temperature forcing systems.
2. Description of the Prior Art
Localized temperature control of electronic components is widely used for military specification qualification, production testing, reliability testing, characterization, environmental stress screening and design verification.
The TP04000 series THERMOSTREAM test system from Temptronic Corporation (Newton, MA) is advertised to be capable of being used for testing components, hybrids, modules, small assemblies and printed circuit boards at temperatures from -75.degree. C. to +225.degree. C. The system includes an integral CRT screen for user interface and a mechanical locking arm that pipes hot and/or cold air at eighteen standard cubic feet per minute (SCFM) to a device-under-test (DUT). Temperature sensing of the airstream is done at the TP04000 system output nozzle, reportedly within one centimeter of the DUT. The manufacturer reports that this assures that the air affecting the DUT is within one degree Centigrade of the displayed temperature. The temperature accuracy and stability for all device types, package styles and power levels is provided by an automated electronic calibration routine. Custom temperature profiling routines including adjustable ramp rate, soak time and cycle sequences with up to twelve temperatures can be created with user menus presented on the CRT screen. Setup files and thermal profile routines can be developed, filed and retrieved from 3.5 inch floppy disks. Four to ten test set parameters can be loaded into main memory (RAM). A DUT control mode provides direct control of the DUT case temperature. A temperature sensor, e.g., a "K" type or "T" type thermocouple, is located on the test socket in contact with the DUT or attached to the device case to sense DUT temperature. A DUT control mode maintains a stable temperature. A change in the power dissipation level of the DUT is compensated for through air temperature control. The operator must manually fine tune the control constants to match the mass of the DUT for the best compromise between minimal overshoot and fastest temperature transition time.
FTS Systems (Stone Ridge, NY) markets a TURBO-JET system for precision temperature cycling from -80.degree. C. to +230.degree. C., using mechanically-refrigerated air at flow rates from five to fifteen SCFM. A microprocessor controller allows program transition rates from 0.1.degree. C./minute to a maximum of 1600.degree. C./minute. Eight separate programs with up to eight segments per program can be stored, including ramp rate, setpoint and soak time. A keypad is used to enter test temperature setpoints and tolerances, calibration values, ramp rates, soak time, air flow rate and device temperature exposure extremes. Test accuracy and repeatability are stated to be .+-.1.0.degree. C., with component stability maintained to .+-.0.1.degree. C. The temperature can also be controlled from the DUT. Ice can build up in the heat exchanger of a refrigeration system operating at -80.degree. C. so the TURBO-JET system uses an integrated drying system comprising a refrigerated air dryer, a water filter, an oil filter, a particle filter and a heatless regenerative air dryer to lower the dew-point temperature of incoming air to below -80.degree. C.
Thus there is a need for a system that automatically determines the best compromise between minimal overshoot and fastest temperature transition time.